Heavy slabs and sheets of material are commonly stacked standing on an edge leaning against an A-frame. To lift the outer slab from the stack, it first must be pivoted away from the adjacent slab until it can be gripped by a lifting device. The angle through which the outer slab must be pivoted depends upon the clearance needed to allow the lifting device to engage the slab. Since the lifting devices almost universally employed are of the scissors (or lazy tongs) variety, the outer slab must be pivoted through a substantial angle. This can be very dangerous for the operator as the heavy outer slab is likely to over-balance and fall. Also, valuable slabs of materials such as marble and granite are likely to break when they fall resulting in considerable financial loss.
Furthermore, it is often necessary to position a slab or panel which has been lifted by a device against a wall or vertical frame to which it is to be secured. Again, the use of scissors-type lifting devices often means that the slab or panel must be propped well off-vertical in a potentially dangerous position while the device is disengaged. Only after the device has been removed is it possible to then tilt the slab or panel to the vertical position in which it is to be fixed. The vertical clearance above the slab or panel for the attachment and/or removal of the scissors-type device also presents substantial problems in practice.